1. Field of the Invention
This invention relates to the destruction of organic materials containing halogen. In one of its more particular aspects this invention relates to a process for destroying halogenated organic materials utilizing a molten salt containing alkaline earth metal compounds.
2. Prior Art
In the destruction of organic materials such as carbonaceous gas, liquid and solid wastes, it has been found desirable to utilize molten salts in order to take advantage of the higher throughput, shorter residence time, and better heat transfer which characterize molten salt processes as well as the uniformity of reaction zone and economy of operation inherent in their use.
Molten salts have been used for conducting various chemical reactions including use as catalysts in hydrocracking processes for decomposing carbonaceous feedstocks with the addition of hydrogen. Molten zinc chloride or zinc chloride mixed with a zinc oxide acceptor has been recommended for this purpose because of the excellent heat transfer characteristics of the molten salt and the continual renewal of fresh catalyst surfaces thereby realized. Another advantage of the use of a molten salt in hydrocracking processes is that contaminants such as catalyst poisons can be withdrawn with a bleed stream of molten salt to allow uninterrupted operation. The use of zinc chloride is not without problems, however, since zinc chloride is highly corrosive at elevated temperatures. Further, hydrocarbons are relatively soluble in molten zinc chloride, which makes separation of the organic and salt phases difficult. In U.S. Pat. Nos. 3,677,932 and 3,736,250 it is suggested that the solubility of hydrocarbons in molten zinc chloride may be substantially reduced by the addition thereto of certain alkali metal halides. These processes are not altogether satisfactory, however, because separation of the hydrocarbon products from the salts is incomplete. Further, the regeneration of such mixed salts is a complex procedure requiring high temperature treatment in a corrosive atmosphere.
Molten salt processes have also used alkali metal carbonates as molten salts.
U.S. Pat. No. 3,708,270 discloses a process for pyrolyzing carbonaceous materials such as solid wastes by use of a molten salt comprising an alkali metal carbonate and from about 1 to 25 wt. % of an alkali metal sulfide.
U.S. Pat. No. 3,845,190 discloses a process for disposing of organic pesticides by means of oxidation in a molten salt comprising an alkali metal carbonate.
U.S. Pat. No. 3,916,617 discloses a process for the partial oxidation and complete gasification of a carbonaceous material such as coal to produce a combustible gas, which utilizes a molten salt comprising an alkali metal carbonate and about 1 to 25 wt. % of an alkali metal sulfide.
U.S. Pat. No. 4,145,396 discloses a process for treating organic wastes containing a radioactive material such as strontium, cesium, iodine or ruthenium with oxygen in a molten salt bath comprising an alkali metal carbonate and from about 1 to 25 wt. % of an alkali metal sulfate.
U.S. Pat. No. 4,246,255 discloses a process for the disposal of polychlorinated biphenyls (PCB's) by oxidation in a molten salt comprising an alkali metal carbonate.
A wide variety of other salts have also been utilized in molten salt processes.
U.S. Pat. No. 3,647,358 discloses the use of ionic, inorganic salts having a melting point in the range of 50.degree. to 600.degree. C. for the oxidation of gaseous, liquid, and solid carbonaceous materials.
Metal recovery has also been realized by means of molten salt processing.
U.S. Pat. No. 3,899,322 discloses a process for recovering valuable metals, particularly noble metals and aluminum, from scrap by introducing metal-containing scrap and oxygen into a molten salt comprising an alkali metal carbonate and about 1 to 25 wt. % of an alkali metal sulfate.
U.S. Pat. No. 4,164,416 discloses a process for recovering copper or lead from a sulfide ore concentrate by introducing the ore concentrate and oxygen into a molten salt comprising an alkali metal carbonate.
While the processes disclosed in the above listed patents are effective for disposing of various wastes and for recovering valuable materials therefrom, none of these processes is wholly satisfactory for treating organic wastes containing halogen. Although the use of alkali metal carbonates provides advantages over other waste disposal methods, the necessity of furnishing alkali metal carbonate make-up to the molten salt bath represents an expense which it would be desirable to reduce.
It is accordingly an object of this invention to provide a more economical process for the destruction of halogen-containing waste materials.
It is another object of this invention to provide such a process wherein very complete destruction of waste materials is obtained by use of a molten salt.
It is another object of this invention to provide such a process wherein the molten salt can be replenished by means of a relatively inexpensive makeup salt material.
It is another object of this invention to provide a process which is effective for the destruction of halogen-containing organic materials and the recovery of metals present therein.
It is another object of this invention to provide a process in which the composition of the molten salt is optimized to provide appropriate physical and chemical properties for the efficient conduct of the waste destruction operation.
It is another object of this invention to provide such a process wherein the halogen content of waste materials is retained in the molten salt.
Another object of this invention is to provide such a process in which practically no halogen-containing compound is emitted in the off gas produced in the process.
It is still another object of this invention to provide a process wherein economical disposal of the spent salt resulting from the molten salt reactions is facilitated.
Other objects and advantages of this invention will become apparent in the course of the following detailed description.